Carbonic anhydrase IX, an endogenous hypoxia marker, expression in head and neck squamous cell carcinoma and its relationship to hypoxia, necrosis, and microvessel density

Carbonic anhydrase M (CA M) is a transmembrane glycoprotein with an active extracellular enzyme site. We have shown previously that if was hypoxia ind ucible and may therefore be an endogenous marker of hypoxia. It is overexpr essed in some tumors, particularly renal cell carcinoma, The aim of this st udy was to examine the expression and localization of CA IX in head and nec k squamous cell carcinoma (HNSCC) and relate this to the location of tumor microvessels, angiogenesis, necrosis, and stage. Expression of CA M was det ermined by immunoblotting in three HNSCC cell lines grown in normoxia and h ypoxia (pO(2) 0.1%) and three paired tumor and normal tissue samples of HNS CC, Archived paraffin sections (79) of HNSCC were immunostained with antibo dies to CA IX and CD34 to determine microvessel density (MVD). By double st aining sections with CA IX and CD34, the distance between blood vessels and the start of CA K expression and necrosis was calculated, CA IX was induce d by hypoxia in ah three HNSCC cell Lines and overexpressed in HNSCC tumor tissue. Overexpression was localized to the perinecrotic area of the tumor on immunostaining, and the percentage area of the tumor expressing CA IX wa s significantly higher with more tumor necrosis (P = 0.001), a high MVD (P = 0.02), and advanced stage (P = 0.033) on univariate analysis and necrosis (P = 0.0003) and MVD (P = 0.0019) on multivariate analysis. The median dis tance between a blood vessel and the start of CA IX expression was, 80 mum (range, 40-140 pm). CA IX is overexpressed in HNSCC because of hypoxia and is a potential biomarker for hypoxia in this tumor. Overexpression may help to maintain the intracellular pH, giving tumor cells a survival advantage and enhancing resistance to radiotherapy and chemotherapy. CA M is a potent ial target for future therapy in HNSCC.